This invention relates to a system for keying discs to a shaft and more particularly to a system for keying blade discs to a shaft in a steam turbine.
In large steam turbines the last stages of the turbine become extremely large with blades in the neighborhood of eight feet long extending from a spindle which is approximately four feet in diameter. Therefore, it is desirable to fabricate the spindle utilizing a relatively small diameter shaft with discs shrunk onto the shaft. Even though the discs are shrunk on the shaft with an interference fit, because of differential heating and the large torque transmitted between the discs and the shaft it has been common practice to key the discs to the shaft. The keys had a rectangular cross-section with relatively sharp corners, which resulted in very high stress concentrations at the corners and after many hours of operation cracks began to form radiating from the corners of the keyways. To reduce the concentration of stresses in the keyways round keys were used and round holes were drilled at the juncture of the discs and shaft as this eliminated the sharp corners in the rectangular keyways and reduced the stress concentration; however, the area adjacent the bore of the discs have very large stresses, the round keys did produce stress concentration, and have resulted in cracking eminating from the round keyways. Therefore, an object of this invention is to eliminate any type of stress concentration in the bore of the discs and prevent relative movement between the discs and the shaft during periods of differential heating.